1. Field of the Invention
The present invention relates to a wireless LAN system, and more particularly to a high-speed wireless LAN system using a combined UWB (Ultra Wide Band) communication method and an optical communication method.
2. Description of the Related Art
Superior mobility and lack of cable connection represent significant advantages of wireless LAN systems over comparable wire-ed LAN systems and wireless LAN systems are becoming more widely used by the general population. Current wireless LAN systems operate in the radio frequency (RF) band of 2.4 GHz or 5 GHz as a carrier, e.g., IEEE 802.11a, b and g, and the selected carrier is modulated to carry the data content. These wireless LAN systems provide a transmission speed of 22 Mbps in the 2.4 GHz band, or a transmission speed of 54 Mbps in the 5 GHz band, respectively.
Under such transmission speeds, however, it is difficult to provide a high-capacity and high-speed service through the existing wireless LAN system due to the bottlenecks that may occur in the home or office. To solve this problem, there has recently been proposed a method that uses an UWB (Ultra Wide Broadband) connection instead of the RF band as a transmission medium. The transmission speed of high-speed wireless LAN systems that uses UWB connection as the transmission medium can be 100 Mbps (Mega bits/sec) or more.
An UWB-based wireless LAN system has the advantage in that it can provide a high-speed and large-capacity service, but its serviceable area is limited typically to less than 10 meters (m). Accordingly, conventional UWB-based wireless LAN systems use one gateway and a plurality of DAP (Dummy Access Point) properly arranged at important points within the network to increase the operating range. The gateway and the DAPs are typically connected together through an optical fiber.
FIG. 1 is a block diagram illustrating an example of the main parts of an UWB-based high-speed optical wireless LAN system. Referring to FIG. 1, the optical wireless LAN system shown includes a gateway sub-module 130, a plurality of access points (APs/DAPs) 120 and a plurality of mobile stations (STAs) 110, e.g., notebook computers. This system configuration may be referred to as a ‘UWB over fiber’ transmission, as the UWB connection is established using an optical fiber connection. In FIG. 1, one AP 120 and one mobile station 110 are illustrated for the convenience of explanation. However, it would be recognized by those skilled in the art that a plurality of APs 120 and stations 110 may be included within a wireless LAN system.
Referring to FIG. 1, the mobile station 110 transmits data modulated in a format according to the UWB communication method, or demodulates data received in the UWB format to the original data. Station 110 includes a UWB module 112 for transmitting/receiving UWB signal through UWB antenna 113. AP 120 also includes UWB antenna 123 through which the AP 120 transmits/receives, wirelessly, the UWB signal to/from the mobile station 110. AP 120 also includes WB optical transmitter/receiver 124 which transmits/receives a UWB signal to/from the gateway sub-module 130 through optical fibers 140, 150. The gateway sub-module 130 includes UWB optical transmitter/receiver 134, which transmits/receives the UWB signal to/from the AP 120 through the optical fiber 150, 140, respectively. UWB module 132 modulates data to be transmitted through the optical transmitter/receiver 134 to a UWB format, or demodulates the data received in the UWB format to the original data. A large-capacity subscriber service can be provided through a Fiber-To-The House (FTTH) connection, wherein gateway sub-module 130 serves to provide services such as multimedia, VOD (Video On Demand), EOD (Education On Demand), AOD (Audio On Demand), etc., to the respective AP (DAP) 120 or directly to terminal, e.g., mobile station 110, without occurring a service collision.
Although not shown in FIG. 1, a UWB signal can be transferred to a plurality of APs 120 arranged at proper points of the LAN controlled by gateway sub-module 130 through the optical fiber. In this case, in order to transmit the UWB formatted signal through the optical fiber, the UWB formatted signal is directly modulated and transmitted, and this method is called the ‘UWB over fiber’. Using the ‘UWB over fiber’ technique, the limited service area can be expanded using the APs 120 arranged at proper points.
The UWB-based high-speed wireless LAN system as described above can perform a high-speed data transmission of 100 Mbps or more by using the UWB formatted signal instead of the RF signal. However, since the UWB formatted signal can easily pass through obstacles, according to the property of the medium, it is potentially in danger of being intercepted and subject to access by unauthorized persons. Hence the security of such UWB systems is considered weak. In order to improve the protection and security characteristic of the UWB system diverse encryption techniques and authentication methods such as WEP (Wired Equivalent Privacy), AES (Advanced Encryption Standard), and WPA (WI-FI Protected Access) are applied to the UWB-based high-speed wireless LAN system. However, such an application of encryption techniques and the authentication methods increases the cost of the UWB system and occupies valuable bandwidth.
Systems using an optical signal, e.g., IR (Infra-Red), have been shown to have a superior security characteristic as the optical or IR signal cannot pass through an obstacle, and thus it is more difficult to intercept. Hence the security of such a system is significantly increased. FIG. 2 represents a block diagram illustrating an example of the main parts of an optical or IR-based wireless LAN system that exhibits a superior security characteristic. The IR wireless LAN system includes a gateway sub-module 230, a plurality of access points (APs) 220, and a plurality of mobile stations 210. Again, as with regard to FIG. 1, only one element of each type is shown for purposes of explanation.
As shown, mobile station 210 is provided with an IR module 226 for transmitting/receiving an IR signal, and AP 220 is provided with an IR optical transmitter/receiver for transmitting/receiving an IR signal to/from the mobile station 210. AP 220 further transmits/receives the IR signal to/from the gateway sub-module 230 through optical fibers 240, 250, respectively. The gateway sub-module 230 includes IR module 236 provided with an IR optical transmitter/receiver 234 for transmitting/receiving the IR signal to/from the AP 220 through the optical fibers 240, 250. Although not shown, it would be recognized that gateway sub-module 230 and the mobile station 210 may directly communicate with each other without passing through the AP 220.
The gateway sub-module 230 modulates a signal inputted from an external network (not shown) onto an IR carrier signal, and transmits the IR carrier signal to the AP 220 through IR optical transmitter/receiver 234. AP 220 receives the IR signal transmitted from the gateway sub-module 230 through IR optical transmitter/receiver 224, and retransmits the IR signal, wirelessly, through optical antenna 221. The IR signal transmitted wirelessly is received in the IR module 216 of the mobile station 210, and then restored to the original signal.
According to the above-described construction, if any one intercepts the IR signal while the IR communication between the AP 220 and the mobile station 210 is performed the IR signal is not received by the mobile station 210, and, thus, by grasping this lack of communication, the user can confirm that interception has occurred.
However, the conventional optical or IR signal has an imposed output power limitation in accordance with an eye-safety regulation. For example, in the case of the IR signal having a wavelength of 650 nm, its output power is limited to less than 0.2 mW. The limit of the output power causes the transmission speed to be limited to less than several Mega bits/second (Mbps), and thus significant limitations in the use of high-speed wireless LAN system using optical or IR communications exist.
In spite of the good mobility and convenience of the wireless LAN system, security concerns limit the use of a UWB wireless LANs in most companies. Since a wireless LAN system, without guaranteed security, causes problems in a company's large-scale introduction of such a wireless LAN system, it is a priority to introduce a wireless LAN system with guaranteed security.
In order to guarantee the security of the wireless LAN system, optical or IR signals may be used instead of the RF signal. However, as described above, in the case of constructing a wireless LAN using the optical or IR signal, the transmission speed is limited to less than several Mbps due to the limit of the output power according to the eye-safety regulation.